Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof withgraphical user interface showing my new design; and,

FIG. 2 is a front view of a second embodiment.

The broken line showing of a display screen or portion thereof forms nopart of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.